This invention relates to the production and use of welding filler metal and, more particularly, to the continuous production of the welding filler metal.
In one type of welding, two or more pieces of metal are heated to their melting points and fused together. Optionally, additional molten metal may be provided as welding filler metal. In another type of welding, the welding filler metal is melted and applied to a face of a substrate as an overlay layer to build up the substrate. This second type of welding is used to repair substrates that have become thinned or damaged during service, or to apply a special facing to the substrate such as a hard facing. In either type of welding, the welding filler metal is melted and fed into the melted region. xe2x80x9cWelding filler metalxe2x80x9d may be of discrete lengths, which are typically used in manual welding operations, or it may be of continuous lengths used in automated welding machines.
A wide variety of methods are used to manufacture welding filler metal, with drawing or rolling being favored for ductile metals such as steels. The methods that may be used to manufacture welding filler metal of titanium aluminides and nickel-base superalloys are limited by the inability of most of these materials to be drawn, rolled, or swaged.
Instead, in conventional commercial practice the titanium aluminide or nickel-base superalloy to be made into a welding filler metal is cast into a rod about 1 inch in diameter. A number of these rods are placed into an extrusion can, and thereafter extruded to about xc2xc inch diameter. The xc2xc inch diameter rods are de-canned, cut to length, placed into another extrusion can, and extruded a second time to about 0.06-0.08 inch diameter. This approach is acceptable technically, but it leads to a high cost of the superalloy welding filler metal. About 30 percent or more of the length of each extrusion is lost due to front-end and tail-end extrusion loss, so that the yield of usable welding filler metal from the double-extrusion process is typically less than 50 percent, and often about 25 percent or less, of the weight of the starting material. As a result, the cost of titanium aluminide welding filler metal is sometimes as much as $1500 per pound, and the cost of superalloy welding filler metal is sometimes as much as $700 per pound.
There is a need for an improved approach to the manufacture of an acceptable quality, economically produced welding filler metal of titanium aluminides and nickel-base alloys such as nickel-base superalloys. The present invention fulfills this need, and further provides related advantages.
The present invention provides a technique for producing and using welding filler metal. The production technique involves a single step of continuously casting to size. The welding filler metal is thereby produced economically and in an acceptable quality. The present approach is operable with a wide variety of welding-filler-metal materials, but it is most advantageously used to produce welding filler metal of materials that cannot be drawn, swaged, or rolled.
A method for welding an article comprises the steps of producing welding filler metal by furnishing a powder of a welding-filler-metal composition, providing a continuous casting mold having a welding-filler-metal diameter, and melting the powder into a top of the continuous casting mold, while withdrawing a continuous length of the welding filler metal in a solid form from a bottom of the continuous casting mold. The welding filler metal may thereafter be used to weld an article by applying a weld overlay layer to a substrate or by joining two articles together using the welding filler metal.
The step of furnishing preferably includes the step of furnishing a powder of a titanium aluminide or a nickel-base superalloy. The continuous casting mold is desirably a water-jacketed continuous casting mold, and desirably has an inner diameter of from about 0.050 inch to about 0.080 inch.
The melting of the powder is preferably accomplished using a laser beam. The laser melting allows the powder to be melted quickly and in a small volume at the top of the casting mold, minimizing oxidation or other damage to the powder prior to its melting and consolidation in the casting mold.
The present approach is most advantageously used to make welding filler metal of materials that must otherwise be made into welding filler metal by casting and multistage extrusion. The conventional weld-rod fabrication technology for these materials significantly increases the cost of the final welding filler metal due to the multiple fabrication stages and the loss of material as scrap during the fabrication operations. The present approach requires the use of the welding filler metal starting material in relatively finely divided form, such as a powder. The remainder of the processing is accomplished relatively inexpensively and in a single continuous melting-and-casting operation. The net cost of preparing welding filler metal by the present approach is significantly less, and estimated to be xc2xc or less, of the cost of producing welding filler metal by the conventional casting-and-multistage-extrusion approach. The welding filler metal produced by the present approach is of sufficient relative density and mechanical properties in the as-cast-rod form that it may be used in either manual or continuous welding operations.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.